The polygalactomannans are polysaccharides composed principally of galactose and mannose untis and are usually found in the endosperm of leguminous seeds, such as guar, locust bean, honey locust, flame tree, and the like. Guar flour, for example, is composed mostly of a galactomannan which is essentially a straight chain mannan with single membered galactose branches. The mannose units are linked in a 1-4-.beta.-glycosidic linkage and the galactose branching takes place by means of a 1-16 linkage on alternate mannose units. The ratio of galactose to mannose in the guar polymer is, therefore, one to two. Guar gum has a molecular weight of about 220,000.
Locust bean gum is also a polygalactomannan gum of similar molecular structure in which the ratio of galactose to mannose is one to four. Guar and locust bean gum are the preferred sources of the polygalactomannans, principally because of the commercial availability thereof.
Polygalactomannan gums swell readily in cold water and can be dissolved in hot water to yield solutions which characteristically have a high viscosity even at a concentration of 1-1.5 percent. Guar gum and locust bean gum as supplied commercially usually have a viscosity (at 1% concentration) of around 1000 to 4000 centipoises at 25.degree. C. using a Brookfield Viscometer Model LVF, spindle No. 2 at 6 rpm.
For a number of commercial applications it is advantageous to have a gum that provides a solution viscosity lower than that imparted by the same gum in the form in which it is ordinarily sold commercially. Thus, for various food products wherein a polygalactomannan is incorporated as a thickener or is used in a gel or jelly-type product, it is desirable to employ a gum which has a one percent solution viscosity between about 1000 to 2000 centipoises at 25.degree. C. Solutions having lower viscosities than those produced with conventional commercial gum are also advantageous in paper making procedures, either in the beater or when used as a sizing. Low viscosity solutions of polygalactomannan gums also find special application in the sizing and printing of textiles.
Further, polygalactomannan gums have found application in chemotherapeutic regimens. U.S. Pat. No. 3,313,800discloses that guar gum has been used for the treatment of certain physiological disorders of the gastro-intestinal tract. Also it has been found effective in treatment of hypercholesteremia. The ordinary dose for humans for hyperchlosteremia is from 3 to 5 grams taken three to four times a day. When it is attempted to incorporate the guar gum into an aqueous medium, the gum hydrates so rapidly that the product soon sets to a semi-solid mass which is not palatable and which is not accepted by human patients. Suspensions of the gum in non-aqueous media such as glycerin have failed to provide a suitable dosage form, as they resulted in adherence of the gum to the oral or tracheal mucosa with subsequent discomfort and difficulty in swallowing and breathing.
It has also been proposed to encapsulate finely divided guar gum into gelatin capsules. This dosage form has the disadvantage of requiring the patient to swallow 4 or 5 large capsules at a time. However, a more important drawback is that when the capsules are swallowed the gastric juices dissolve the gelatin and begin to hydrate the outside of the gum contained therein, forming a hydrated shell, which acts as a barrier to further penetration and which results in imperfect use of the guar gum. The same problem is presented by tablets and, as a result, neither of these methods of incorporation have proven to be practical.
It is desirable to provide modified guar gum which disperses readily in aqueous media and which hydrates sufficiently slow so that an aqueous media dispersion remains fluid for a period between about 15 and 45 minutes and is adequate for oral use.
There is also need for novel polysaccharidic derivatives which have properties uniquely adapted for highly specialized application as ultrathin semipermeable reverse osmosis membranes. U.S. Pat. No. 3,580,841 describes the disadvantages of conventional semipermeable membranes when employed in the purification of saline water by reverse osmosis. A superior semipermeable membrane must possess a favorable selectivity to the desired product solvent and a high degree of rejection toward the solute. Such membrane should also be coherent, structurally stable, and permit a minimum of viscous flow under reverse osmosis conditions.
Accordingly, it is an object of the present invention to provide polygalactomannan gum derivatives which exhibit solution viscosities that are lower than those imparted by the same gums in the conventional commercial forms.
It is another object of the present invention to provide guar gum esters which are slowly hydratable and readily dispersible in water.
It is a further object of the present invention to provide a novel class of polygalactomannan gum formate esters.
It is still another object of the present invention to provide one or more processes for producing polygalactomannan gum formate esters.
Other objects and advantages shall become apparent from the following description and examples.